<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>Форма</title>
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-
beta.3/css/bootstrap.min.css" integrity="sha384-
Zug+QiDoJOrZ5t4lssLdxGhVrurbmBWopoEl+M6BdEfwnCJZtKxi1KgxUyJq13dy" crossorigin="anonymous">
  <style>
    .form-wrap {
      margin: auto;
      padding: 20px;
      max-width: 800px
    }

    .error {
      border: 2px solid red;
    }
  </style>
</head>

<body>
  <div class="form-wrap">
    <form class="my-form" action="#">
      <div class="form-row">
        <div class="form-group col-md-6">
          <input type="text" id="name" class="form-control" placeholder="Имя">
          <div class="invalid-feedback name">Имя должно состоять из букв</div>
        </div>
        <div class="form-group col-md-6">
          <input type="text" id="phone" class="form-control" placeholder="+79999999999">
          <div class="invalid-feedback phone">Не верный формат номера</div>
        </div>
      </div>
      <div class="form-row">
        <div class="form-group col-md-6">
          <input type="password" id="password" class="form-control" placeholder="Пароль">
          <div class="invalid-feedback passwd">Введите пароль</div>
        </div>
        <div class="form-group col-md-6">
          <input type="password" id="password_repeat" class="form-control" placeholder="Повторите пароль">
          <div class="invalid-feedback passwd_rep">Пароли не совпадают</div>
        </div>
      </div>
      <button type="submit" class="btn btn-primary">Отправить</button>
    </form>
  </div>

  <script src="script.js"></script>
</body>

</html>